1. Field of the Invention
The present invention concerns a purgeable manifold system for the movement of low pressure chemicals. More specifically, this invention concerns a manifold system that may be purged efficiently, because potential areas of entrapment of the low vapor pressure chemicals are removed, and that is simple to construct.
2. Description of Related Art
Certain manufacturing processes require the use of low vapor pressure chemicals at high purity levels. One example is semiconductor manufacturing, which requires the distribution of highly reactive, low vapor pressure chemicals in ultra-pure conditions, in order to avoid unwanted contamination during the fabrication process and to maintain competitive process yields. These low vapor pressure chemicals include, among others, organo-metallic precursors such as tetrakis(dimethylamido) titanium (TDMAT), tetrakis(diethylamino) titanium (TDEAT), tantalum pentaethoxide (TAETO), copper hexafluoroacetylacetonate-trimethylvinylsilane (Cu(hfac)TMVS), tetramethyltetracyclosiloxane (TMCTS), tetraethyl ortosilicate (TEOS), and trimethylphosphate (TMP). Typically, these low pressure chemicals are stored in container having a capacity varying from 100 milliliters to 200 liters and known by a variety of common and trade names such as “canisters,” “ampoules,” or “hosts”, and are delivered to chemical vapor deposition (CVD) process tools, either by direct liquid injection (DLI) process or by a “bubbler” process.
With DLI, the low vapor pressure chemical is delivered to a process tool by injecting a push gas (generally, an inert gas such as nitrogen or helium) through a first manifold into the container, in the headspace above the low vapor pressure chemical in liquid state. The increase in gas pressure inside the container causes the low vapor pressure chemical to be ejected from the container through a diptube immersed in the chemical and then through a second manifold connected to the container, and to be delivered eventually to the process tool.
With the “bubbler” process, a push gas (generally, an inert gas such as nitrogen or helium) is injected into the container through a first manifold connected to the container and through a diptube immersed in the low vapor pressure chemical, which is supplied to the container as a liquid by pressurized gas delivery through a second manifold. The container is heated, in order to increase vapor pressure and to saturate the bubbling gas with vaporized chemical, and the bubbling mixture of gas and chemical is then ejected from the container through a third manifold and delivered to a process tool.
From time to time, it is necessary to replace and clean the container, for instance, due to maintenance requirements, or due to decomposition of the low vapor chemical within the container caused by the applied heat, or for other reasons. Before detaching the container from the process chemical delivery lines, the low vapor pressure chemical must be completely removed from the points of connection between the manifold valves and the process lines. Typically, the low vapor pressure chemical is evacuated and purged through a multi-step procedure comprising sequences of blow cycles, which push the residual chemical into the container, and of vacuum cycles, which vaporize and remove the chemical particles trapped into the manifolds. Due do the high level of decontamination required, this procedure is extremely time consuming and affects process yields significantly. Therefore, there is a need for a manifold system that can be purged with reduced cycle times.
Moreover, purge gas is sometimes blown into the container with high flow rates, generating a spray, which may not only be drawn into the manifolds with a detrimental effect on process efficiencies due to the introduction of liquid chemical into the manifolds and to the increase in the time required to remove the chemical, but which may also be detrimental over time to the manifolds and to the vent lines. Therefore, there is a need for a purgeable manifold system that will reduce this spray effect.
Different invention have been disclosed in the prior art addressing the above needs to different degrees. U.S. Pat. No. 5,964,230 and U.S. Pat. No. 6,138,691, both to Voloshin et al., teach a solvent purging system that not only adds complexity to the purging procedure, but that also creates the additional requirement of expensive decontamination of highly toxic chemicals from the solvent.
U.S. Pat. No. 6,431,229 to Birtcher et al. discloses a solventless, purgeable, diaphragm valved manifold for low vapor pressure chemicals, comprising a block valve assembly that includes two diaphragm valves. There remains a dead space between the two valves in the valve block assembly, which complicates cleaning and which requires longer purge cycles in order to remove the chemical from that dead space.
U.S. Pat. No. 6,648,034 to Birtcher et al. teaches a purgeable manifold for low pressure chemical containers, with similar features and drawbacks as the invention taught in U.S. Pat. No. 6,431,229.
U.S. Patent Application 2003/0131885 to Birtcher et al. discloses a cabinet for chemical delivery with solvent purging, which includes some of the features and drawbacks of the inventions disclosed in U.S. Pat. Nos. 6,138,691 and 6,431,229.
Japanese Patent JP 2004-063833 A to Yoshitome Koichi teaches a low pressure chemical supply system for use in a CVD process, comprising a manifold block fed by entry and exit valves and containing a bypass route with two additional valves. While this invention appears to offer process improvements over the invention disclosed in U.S. Pat. No. 6,431,229, this supply system still contains dead spaces where the low pressure chemical may be trapped, requiring extended purge cycles.
None of the above inventions appears to disclose a purgeable manifold system that eliminates dead spaces and costly specialty valves, and that reduces purge cycles and the manifold contamination caused by chemical spray.